Method for manufacturing a head for recording and reading optical data

ABSTRACT

A method of manufacturing a head for recording and reading optical data. The method includes: providing a silicon substrate on which a silicon oxide film and a silicon deposition layer are stacked; etching the bottom of the silicon substrate by a given depth to form an opening; forming an aperture having a given slant angle in the silicon deposition layer located on the opening; etching the portion of the silicon oxide film, exposed through the opening; forming a dielectric layer on the silicon deposition layer including the aperture; removing an exposed portion of the bottom of the silicon deposition layer by a given thickness to expose a portion of the dielectric layer, forming a probe on the exposed portion of the dielectric layer and the silicon deposition layer exposed through the opening; and burying the aperture with a non-linear material.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to a head for recording/reading opticaldata and method of manufacturing the same, and more particularly to, ahead for recording/reading optical data and method of manufacturing thesame capable of improving throughput of a laser beam passing throughapertures in order to record/read data in a probe type mode (AFM mode)(Atomic Force Microscopy) and a NSOM (Near-Field Scanning OpticalMicroscopy) mode.

2. Description of the Prior Art

In order to store more information per unit area in an optical storagedevice, it is required that the wavelength of a recording optical sourcebe reduced or the numerical aperture of a condensing lens must beincreased. To satisfy such a requirement, it may be considered todevelop a blue laser diode (LD) and to increase the numeral aperture upto 1.0. In these cases, however, there is a limit that information isrecorded with a high density due to diffraction of light, in a nextgeneration information storage device requiring a high-densityrecording.

As an option for overcoming this limit, there are a SPR (Scanning ProbeRecording) technology using a probe of AFM (Atomic Force Microscope), anultra-resolution medium technology, a technology using a Near-FieldScanning Optical Microscopy (NSOM) probe that overcomes the diffractionlimit of light and the like.

As a first example of a prior art, a technology using a NSOM opticalfiber probe employs a laser light outputted to an aperture having a verysmall size (aperture: several dozens˜several hundreds of nm). In case ofthe NSOM optical fiber probe, however, it is mechanically very fragileand is not easy to arrange it in plurality at a time. Further, asthroughput of light outputted to the aperture is very small (generallyabout 10⁻⁵˜10⁻⁷ in cases of an aperture having 100 nm in size), the NSOMoptical fiber probe is very difficult to be actually used in view ofrecording and data processing speed.

In other words, in order to use the NSOM optical fiber probe in anoptical storage device, an aperture having a high throughput is requiredand a probe arranged in plurality and not easily abraded mechanically isrequired.

A second example of a prior art has a probe having a plurality ofapertures through a semiconductor process (FIG. 1).

Referring now to FIG. 1, there are formed a plurality of holders 11 areprovided. Probes 12 formed of a thin metal film are formed at the bottomof the holders 11. Apertures 13 are formed between the probes 12. Evenin this case, however, as transmissivity of a laser beam outputted fromthe apertures 13 of the probes 12 is below 10⁻⁵ as in conventionaloptical fiber probe, it is required that transmissivity be increased. Amethod of improving throughput of light transmitted into a hole at anend portion of the probes 12 includes a method of exciting plasmon, amethod of minimizing an optical loss region generated from onewavelength size at the end portion, etc.

The third example of a prior art attempted to improve throughput of theaperture by a method of exciting plasmon. Plasmon Mode, however, it isdifficult to effectively excite plasmon since its exciting efficiencydepends on the polarization of an incident beam. In order to moreeffectively excite plasmon, there is a need for an aperture structure bywhich plasmon can be effectively excited through a special process.

A fourth example of a prior art include a method of making an aperturestructure having a high throughput by making an end portion of the probeminimize an optical loss region. The method of minimizing the opticalloss region, that is a method introduced in a conventional optical fiberprobe, makes the aperture having a very large cone angle through amulti-step wet etching process. A reflection film for reflecting anincident light is located in a first taper region and a reflection filmhaving a very large cone angle is located in a second taper region, sothat the optical loss region can be reduced by maximum. Also, a verysmall aperture having a probe shape is positioned in a third taperregion to form an aperture of high throughput. In this case, however, asthe size of the aperture representing an optimum high throughput isdefined depending on the first taper region and the aperture ismanufactured by a multi-step wet etch process, there is a problem thatits manufacturing process is complicated. Further, there is a problemthat it could not be applied to an optical storage device of a probemode since the end portion of the probe is very large.

Meanwhile, a fifth example of a prior art includes a method ofmanufacturing an aperture of a high throughput using semiconductorprocess and wet etch process. The method manufactures a probe the endportion of which has a parabolic structure of a very large cone anglethrough anisotropic etching process to silicon, a low-temperature oxidefilm formation process, a deposition process of Cr and a wet etchingprocess in order to minimize the optical loss region. In case of thisstructure, however, as the process of manufacturing the probe includingthe low-temperature oxide film formation process is complicate, there isa problem that it is difficult to make the end portion of the probe in aparabolic shape.

The conventional arts so far attempted to improve throughput by makingan actual object. However, there is a method by which a method similarto a method of manufacturing the aperture having a large cone angle isapplied to a semiconductor process conceptually.

Referring now to FIG. 2, a sixth example of a prior art will beexplained. A relatively large aperture (1 micron to 2 micron) is formedby a silicon semiconductor process and a reflection film is coated,where this structure corresponds to the first taper region mentioned inthe fourth example of a prior art. At this time, a hole having a verysmall size (60 nm) is formed at the center of the reflection film toform an aperture of a high throughput. At this time, a non-linear thinfilm is additionally coated on the reflection film and self-focusingbeing a non-linear characteristic is generated through the nonlinearthin film, thus additionally improving the optical throughput of theaperture.

However, this method includes first forming a reflection film in thefirst taper region and then forming an aperture in the reflection filmto form the aperture of a high throughput. However, this method isalmost impossible to be used. The reason is that a mode of lightreflected by the reflection film could not be effectively transferred toa mode existing in the aperture using only the first reflection film.Also, in this case, there is a region having a large light loss same toa conventional optical fiber probe. Further, though a thin film forcausing self-focusing is additionally coated on the reflection film,there actually occurs no any self-focusing phenomenon. The reason isthat the refractive index varies spatially in an already-formedstructure since the refractive index is spatially different depending onthe non-linear characteristic. Due to this, the difference in the phasedelay is spatially generated to change the size and shape of beam, sothat the amount of beam can be increased since a defocusing phenomenonnot self-focusing can be generated. In other words, as the structure inwhich the non-linear thin film is coated on the reflection film has alimit to reduce the amount of beam (about one wavelength), throughput oflight is not so increased. Further, this structure has a structure inwhich the end portion of the probe is very flat not a probe shapestructure. Therefore, there is a problem that this structure could notbe applied to an optical storage device using the probe mode though itcould be simultaneously applied to the probe mode and the near-fieldscanning optical microscopy.

SUMMARY OF THE INVENTION

The present invention is contrived to solve these problems and an objectof the present invention is to provide a head for recording/reproducingoptical data that generates self focusing and in which an aperture isfully filled with a material having a three dimension non-linearcoefficient, and method of manufacturing the same, which can reduce theamount of beam by about half wavelength, focus beam in a parabolic shapehaving almost no optical loss to effectively excite a near-fieldscanning optical microscopy to the aperture at an end portion of a probeand improve the throughput of the probe than several hundreds times thana conventional optical fiber probe.

In order to accomplish the above object, a head for recording/readingoptical data according to the present invention is characterized in thatit comprises a plurality of apertures formed in a silicon depositionlayer an end portion of which is connected to a silicon substrate, aplurality of probes formed at the bottom of the silicon deposition layerat a region where the plurality of the apertures are formed, and anon-linear material buried within the plurality of the apertures.

A head for recording/reading optical data according to anotherembodiment of the present invention is characterized in that itcomprises a silicon layer an end portion of which is connected to asilicon substrate and the bottom of which has a probe shape, a pluralityof apertures formed in the silicon layer of the probe shape, a thinmetal film formed on the silicon layer including the plurality of theapertures, and a non-linear material buried within the plurality of theapertures.

A method of manufacturing a head for recording/reading optical dataaccording to another embodiment of the present invention ischaracterized in that it comprises the steps of providing a siliconsubstrate on which a silicon oxide film and a silicon deposition layerare stacked; etching the bottom of the silicon substrate by a givendepth to form an opening; forming an aperture having a given slant anglein the silicon deposition layer located on the opening; forming a provein the silicon deposition layer around the aperture exposed through theopening; and burying the aperture with a non-linear material.

The non-linear material generates a self-focusing phenomenon and is madeof a material a third non-linear coefficient of which is very great. Thenon-linear material is made of As₂S₃ and is buried at the temperature ofabout 120° C.

The present invention discloses a head for recording/reading opticaldata having an aperture of a high transmissivity by which an opticalthroughput of a probe necessary to record and reproduce optical data isimproved by over 100 times compared to a conventional optical fiberprobe using a self-focusing phenomenon, and method of manufacturing thesame.

Further, the present invention can manufacture an aperture throughput ofwhich is improved, by effectively optically inducing its effect througha simple semiconductor process without mechanically changing a structureof a probe end portion through a multi-step semiconductor process as ina prior art, in order to improve throughput. In addition, the presentinvention can manufacture an aperture of a high throughput that can bearranged in plurality.

Additionally, the aperture the throughput of which is improved using aself-focusing phenomenon can be applied in manufacturing a probe typenear-field scanning optical microscopy that is arranged in plurality.The aperture can also be applied to a probe type head where a dielectricmaterial film is formed in the aperture and a thin metal film is thenformed on the dielectric material film. Therefore, the present inventioncan be applied both to a probe type mode (AFM mode: Atomic ForceMicroscopy) and a NSOM (Near-Field Scanning Optical Microscopy) mode.

BRIEF DESCRIPTION OF THE DRAWINGS

The aforementioned aspects and other features of the present inventionwill be explained in the following description, taken in conjunctionwith the accompanying drawings, wherein:

FIG. 1 is a cross-sectional view of a probe having a plurality ofapertures;

FIG. 2 is a cross-sectional view of a conventional near-field scanningoptical microscopy (NSOM) optical head;

FIG. 3 is a perspective view of a head for recording/reproducing opticaldata according to the present invention;

FIG. 4 a to FIG. 4 i are cross-sectional views for explaining a methodof manufacturing a head for recording/reproducing optical data accordingto the present invention;

FIG. 5 shows a state showing a self-focusing phenomenon generated withinapertures in which a non-linear material is buried;

FIG. 6 is a characteristic graph illustrating the throughput dependingon the size of the apertures;

FIG. 7 is a perspective view of a head for recording/reproducing opticaldata according to another embodiment of the present invention; and

FIG. 8 a to FIG. 8 g are cross-sectional views for explaining a methodof manufacturing a head for recording/reproducing optical data accordingto another embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention will be described in detail by way of a preferredembodiment with reference to accompanying drawings, in which likereference numerals are used to identify the same or similar parts.

FIG. 3 is a perspective view of a head for recording/reproducing opticaldata according to the present invention.

Referring now to FIG. 3, the head for recording/reading optical data ismainly divided into two sections: a lower structure and an upperstructure. The lower structure includes a silicon substrate 21 andfinally becomes a holder of the head. The upper structure has areverse-trapezoid shape and includes a probe having a plurality ofapertures 25 filled with a non-linear material 28 and a thin metal film27, wherein an end portion of the probe is connected to the lowerstructure.

The upper structure further includes a silicon deposition layer 23. Asilicon oxide film 22 is formed at the boundary of the lower structureand the upper structure. A plurality of the probes having the thin metalfilm 27 are formed at the bottom of the upper structure. A portion ofthe non-linear material 28 filled in the aperture 25 of areverse-trapezoid shape by etching process, formed in the silicon deposition layer 23, is exposed toward the bottom of the silicondeposition layer 23 included in the upper structure.

A method of manufacturing the head for recording/reproducing opticaldata will be below described.

FIGS. 4 a through 4 i are cross-sectional views for explaining a methodof manufacturing the head for recording/reproducing optical dataaccording to the present invention, which shows a process ofmanufacturing the head for recording/reproducing optical data takenalong lines X—X′ in FIG. 3 step by step.

Referring now to FIG. 4 a, a silicon oxide film 22 is formed on asilicon substrate 21. Then, silicon is deposited on the silicon oxidefilm 22 to form a silicon deposition layer 23. First and second nitridefilms 24 a and 24 b are formed at the bottom of the silicon substrate 21and the top of the silicon deposition layer 23. Next, the first nitridefilm 24 a formed at the bottom of the silicon substrate 21 is patternedto expose a given portion of the bottom of the silicon substrate 21. Atthis time, the width of the exposed silicon substrate 21 is 1˜10 mm².

In the above, it should be understood that a silicon oxide film or asilicon nitride film might be used instead of the nitride film.

Referring now to FIG. 4 b, the bottom of the exposed silicon substrate21 is etched by a first etch process. The bottom of the siliconsubstrate 21 is etched in about 100˜1000 μm and an oblique plane 21 abecomes (111) of silicon.

The first etch process is performed with a wet etch, by which a giventhickness of the silicon substrate 21 remains from the silicon oxidefilm 22. This is to physically protect the silicon deposition layer 23since the thickness of the silicon deposition layer 23 is relativelythinly formed than the thickness of the silicon substrate 21.

Referring now to FIG. 4 c, the second nitride film 24 b formed on thetop of the silicon deposition layer 23 is patterned to expose a givenregion of the silicon deposition layer 23. Then, a second etch processis performed to form a plurality of apertures 25 (only one is shown inthe drawing).

At this time, the second etch process is performed with a wet etch. Theaperture 25 has a reverse-trapezoid shape by a recipe of the second etchprocess. The silicon oxide film 22 is exposed at the bottom of theaperture 25. At this time, etching is performed at the bottom of thesilicon substrate 21 where the first nitride film 24 a is not formed, sothat the remaining silicon substrate is removed and the bottom of thesilicon oxide film 22 is exposed. Thus, the silicon substrate 21 isdivided centering on the aperture 25.

A lower base of the aperture 25 is 10˜100 nm in size and the top of theaperture 25 is 1 μm˜100 μm in size. At this time, the depth of theaperture 25 functioning as a waveguide is 1 μm˜10 μm.

Referring now to FIG. 4 d, the first and second nitride films 24 a and24 b and the silicon oxide film 22 exposed at the bottom of the siliconsubstrate 21 are removed.

Referring to FIG. 4 e, a dielectric film 26 is formed on the silicondeposition layer 23 including the aperture 25. The dielectric film 26 isformed to be a pattern through which a given region of the silicondeposition layer 23 between the aperture 25 and another aperture (notshown) is exposed.

Referring now to FIG. 4 f, the exposed portion of the bottom of thesilicon deposition layer 23 is removed by a given thickness by means ofan etch process. The top of the silicon deposition layer 23 is notetched by the dielectric film 26. The silicon deposition layer 23 at aregion between the aperture 25 where the dielectric film 26 is notformed and another aperture (not shown) is completely etched/removed. Atthis time, the dielectric film 26 formed in the aperture 25 is notetched to have a reverse-trapezoid shape intact.

Referring now to FIG. 4 g, a thin metal film 27 is formed on both thebottoms of the silicon deposition layer 23 and the dielectric film 26.Thus, a probe consisting of the thin metal film 27 is formed.

The thin metal film 27 is formed to overcome the diffraction limitoptically and is formed using aluminum in thickness of about 100 nm.

Referring now to FIG. 4 h, a non-linear material 28 is buried into theaperture 25.

The non-linear material 28 is a material that can generate aself-focusing phenomenon and is made of a material a third non-linearcoefficient of which is very great. The material that is great in athird non-linear coefficient includes AS₂S₃. The temperature when theaperture 25 is filled with AS₂S₃ is about 120° C. At this time, as beamcould not be self-focused by about one wavelength size if the aperture25 is not completely buried when the non-linear material 28 is buried,the aperture 25 is completely buried with the non-linear material 28.

Referring now to FIG. 4 i, the silicon substrate 21, the silicon oxidefilm 22 on the silicon substrate 21, the silicon deposition layer 23 andthe dielectric film 26, at one side, are removed. Thus, the head forrecording/reproducing optical data shown in FIG. 3 is completed.

The shape of beam reaching around the aperture 25 of about below 100 nmin size formed in the silicon deposition layer 23 by the above processis determined by the amount of beam, the intensity of an incident beamand the amount of a third non-linear coefficient. In order to form theaperture 25 having a high transmissivity, it is required that the shapeof beam reaching around the aperture 25 have a shape having a parabolicstructure the cone angle of which is very large.

FIG. 5 shows a state showing a self-focusing phenomenon generated withinapertures in which a non-linear material is buried.

Referring now to FIG. 5, the aperture 25 filled with a non-linearmaterial 28, the beam reaching a lower base of the aperture 25 isincident at an angle of θ f greater than θ and has a parabolic structurehaving a very large cone angle. Also, it could be seen that the amountof beam has about half wavelength. Therefore, the aperture 25 can have ahigh throughput that is improved by several hundreds times than thethroughput of a conventional optical fiber probe.

As a result, in order to improve the throughput of the aperture 25, thebeam reaching a lower base of the aperture 25 must be incident in aparabolic structure having a very large cone angle, as shown in FIG. 5.

FIG. 6 is a characteristic graph illustrating the throughput dependingon the size of the apertures.

Referring now to FIG. 6, it could be seen that the throughput of theaperture is improved by over several hundreds times by the calculatedthroughput.

FIG. 7 is a perspective view of a head for recording/reproducing opticaldata according to another embodiment of the present invention; and

Referring now to FIG. 7, a head for recording/reproducing optical datais mainly divided into two sections; a lower structure and an upperstructure. The lower structure includes a silicon substrate 61 andfinally becomes a holder of the head. The upper structure includes aplurality of aperture 65 filled with a non-linear material 68 having areverse-trapezoid shape. The bottom of the upper structure has a probestructure and actually functions as a probe 63 a and the end portion ofthe upper structure is connected to the lower structure.

As in FIG. 3, the upper structure further includes a silicon depositionlayer 63. A silicon oxide film 62 is formed at the boundary of the lowerstructure and the upper structure. A part of the non-linear material 68buried in the aperture 65 of a reverse-trapezoid shape, formed in thesilicon deposition layer 63 by an etch process, is exposed toward thebottom of the silicon deposition layer 63 in the upper structure. Thedifference from the head for recording/reproducing optical data shown inFIG. 3, is that additional probe need not be formed using a thin metalfilm since the bottom of the silicon deposition layer 63 is formed to bea probe type shape by an etch process. As a result, as the silicondeposition layer 63 functioning as the holder of the probe functions asa probe, the holder of the probe and the probe are integrally formed.

A method of manufacturing the head for recording/reproducing opticaldata will be below described.

FIGS. 8 a through 8 g are cross-sectional views for explaining a methodof manufacturing the head for recording/reproducing optical dataaccording to another embodiment of the present invention, which shows aprocess of manufacturing the head for recording/reproducing optical datataken along lines Y-Y′ in FIG. 7 step by step.

Processes shown in FIGS. 8 a through 8 d are same those shown in FIG. 4a to FIG. 4 e. Thus, the explanation will be omitted for the purpose ofsimplicity.

Referring now to FIG. 8 e, a portion exposed at the bottom of thesilicon deposition layer 63 is removed by a given thickness by means ofan etch process, wherein the bottom of the silicon deposition layer 63is etched along the slant angle of the aperture 65 while a portion wherethe aperture 65 is formed has a given thickness. Thereby, a probe 63 aincluding the silicon deposition layer 63 of a given thickness is formedat the bottom of the aperture 65.

At this time, the top of the silicon deposition layer 63 is not etchedby a dielectric film 66, and the silicon deposition layer 63 at a regionbetween the aperture 65, where the dielectric film 66 is not formed, andanother aperture is completely removed.

Referring now to FIG. 8 f, a thin metal film 67 is formed on thedielectric film 66 including the region where the aperture 65 is formed.Next, the aperture 65 is completely filled with a non-linear material68.

The thin metal film 67 is formed to further improve the throughput ofthe aperture 65 and is formed in thickness of about 100 nm usingaluminum.

The non-linear material 68 is a material that can generate aself-focusing phenomenon and is made of a material a third non-linearcoefficient of which is very great, as described with respect to FIG. 4h. For example, the aperture 65 is completely buried using AS₂S₃ thatmaintains the temperature of about 120° C. and is great in the thirdnon-linear coefficient. At this time, as beam could not be self-focusedby about one wavelength size if the aperture 65 is not completely buriedwhen the non-linear material 68 is buried, the aperture 65 is completelyburied with the non-linear material 68.

Referring now to FIG. 8 g, the silicon substrate 61, the silicon oxidefilm 62 on the silicon substrate 61, the silicon deposition layer 63 andthe dielectric film 66, at one side, are removed. Thus, the head forrecording/reproducing optical data shown in FIG. 7 is completed.

Similarly, the shape of beam reaching around the aperture 65 of aboutbelow 100 nm in size formed in the silicon deposition layer 63 by theabove process is determined by the amount of beam, the intensity of anincident beam and the amount of a third non-linear coefficient.

As mentioned above, the present invention has advantages that it canimprove the transmissivity by burying an aperture with a non-linearmaterial and can record/read optical data at a high speed usingapertures arranged in plurality. For example, if the size of theaperture is about 50 nm, the recording density may be several Gigabit/inch², which surpasses a current information storage capacity. Also,the aperture of a high throughput can be used for physical properties ofa high resolution as well as a head of a high-density opticalinformation storage device and the like.

The present invention has been described with reference to a particularembodiment in connection with a particular application. Those havingordinary skill in the art and access to the teachings of the presentinvention will recognize additional modifications and applicationswithin the scope thereof.

It is therefore intended by the appended claims to cover any and allsuch applications, modifications, and embodiments within the scope ofthe present invention.

1. A method of manufacturing a head for recording and reading opticaldata, comprising the steps of: providing a silicon substrate on which asilicon oxide film and a silicon deposition layer are stacked; etchingthe bottom of said silicon substrate by a given depth to form anopening; forming an aperture having a given slant angle in said silicondeposition layer located on said opening; etching a portion of saidsilicon oxide film, the portion exposed through the opening; forming adielectric layer on said silicon deposition layer including saidaperture; removing an exposed portion of the bottom of said silicondeposition layer by a given thickness to expose a portion of saiddielectric layer; forming a probe on the exposed portion of saiddielectric layer and said silicon deposition layer around said apertureexposed through said opening; and burying said aperture with anon-linear material.
 2. A method of manufacturing a head for recordingand reading optical data as claimed in claim 1, wherein the siliconsubstrate remaining in said opening is completely removed in the processof forming said aperture.
 3. A method of manufacturing a head forrecording and reading optical data as claimed in claim 1, wherein saidaperture has a reverse-trapezoid shape in which the length of a lowerplane of said aperture is 10˜100 nm and the length of an upper plane ofsaid aperture is 1 μm˜100 μm.
 4. A method of manufacturing a head forrecording and reading optical data as claimed in claim 1, wherein saidprobe is made of a thin metal film.
 5. A method of manufacturing a headfor recording and reading optical data as claimed in claim 1, whereinsaid non-linear material induces a self-focusing phenomenon and is madeof a material of a third non-linear coefficient.
 6. A method ofmanufacturing a head for recording and reading optical data as claimedin claim 1, wherein said non-linear material is made of As₂S₃ and isburied at the temperature of about 120° C.
 7. A method of manufacturinga head for recording and reading optical data as claimed in claim 1,further comprising a step of forming a thin metal film on saiddielectric layer including said aperture after said probe is formed. 8.A method of manufacturing a head for recording and reading optical dataas claimed in claim 4, or 7, wherein said thin metal film is made ofaluminum.
 9. A method of manufacturing a head for recording and readingoptical data, comprising the steps of: providing a silicon substrate onwhich a silicon oxide film and a silicon deposition layer are stacked;etching the bottom of said silicon substrate by a given depth to form anopening; forming an aperture having a given slant angle in said silicondeposition layer located on said opening; etching a portion of saidsilicon oxide film, the portion exposed through the opening; forming adielectric layer on said silicon deposition layer including saidaperture; removing a portion of the bottom of said silicon depositionlayer to form a probe under said dielectric layer of said aperture, saidprobe having the same slant angle as that of said aperture; and buryingsaid aperture with a non-linear material.
 10. A method of manufacturinga head for recording and reading optical data as claimed in claim 9,further comprising a step of forming a thin metal film on saiddielectric layer including said aperture after said probe is formed. 11.A method of manufacturing a head for recording and reading optical dataas claimed in claim 9, wherein the silicon substrate remaining in saidopening is completely removed in the process of forming said aperture.12. A method of manufacturing a head for recording and reading opticaldata as claimed in claim 9, wherein said aperture has areverse-trapezoid shape in which the length of a lower plane of saidaperture is 10˜100 nm and the length of an upper plane of said apertureis 1 μm˜100 μm.